Signal Indicator Circuit; Tuning Indicator Circuit - Pioneer SX-3800 Service Manual

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S I G N A L l n d i c a t o r C i r c u i t
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F i g . 4 - 7 S I G N A L i n d i c a t o r d r i v e c i r c u i t
The SX-3800 SIGNAL indicator consists of an
FL tube 5-point indicator display. The signal meter
drive signal obtained from the FM IF system IC
(PA300?-A) and AIVI tuner IC (HA119?) is first
amplified and then applied to the indicator drive
IC (HA12010). This IC contains 12 pairs of voltage
comparators similar to those employed in the
power indicator circuit, b of these pairs being used
to drive the SIGNAL indicator.
T U N I N G l n d i c a t o r C i r c u i t
The TUNING indicator consists of a center
tuning indicator (which lights up when a broad-
casting station frequency is properly tuned) and
2 detuning direction indicators which indicate the
direction in which the station has been tuned awav
from. The corresponding drive circuits are outlinei
in Fig. 4-B below.
The TUNING indicator is activated once the
station has been tuned to within t100kHz of the
center frequency. This is because
e16 is turned on
and Q21 turned off (resulting in the detector
dif_
feren^tial amplifier le19 & e20J being tumed
off
and Q24 being turned on) by the FM muting signal
appearing at pin no.lB of the IF system IC
{PA3007-A) and passed via the Schmitt circuit
(Q17 & Q1B) rvhen the station is tuned
away by
m o r e t h a n t 1 0 0 k H z .
The DC voltage on pin no.4 of pAB007_A
de-
scribes an S curve when tuning to and away from
a
particular broadcasting frequency, the voltage
on
pin no.2 serving as the reference level. This
DC
Fig. 4-8 TUNING indicator drive.circuit
voltage is amplified by the differential amplifier
(Q19 & Q20) and then applied to a polarity detec_
tor switch circuit (eZZ & e2g).
When tuning to a frequency from the high fre_
quency side (or tuning away from the frequency
to a higher frequency), the voltage on pin no.4 will
be higher than that on pin no.2. The e20 collector
voltage will thus be lowered and the
e1.g collector
voltage raised, resulting in e2B being tumed on,
and the higher frequency (right hand side) detun-
ing direction indicator also being turned on. When.
SCHMITT
C I R C U I I
rc (PA30(r/-A )